This application relates generally to gas turbine engines and, more particularly, to gas turbine combustors.
Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Pollutant emissions from industrial gas turbines are subject to Environmental Protection Agency (EPA) standards that regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). In general, engine emissions fall into two classes: those formed because of high flame temperatures (NOx), and those formed because of low flame temperatures, which do not allow completion of the fuel-air reaction (HC & CO). At least some known gas turbines use dry-low-emissions (DLE) combustors that create fuel-lean mixtures that facilitate reducing NOx emissions from the engines while maintaining CO and HC emissions at low levels.
The combustion of the fuel/air mixture inside a gas turbine engine combustor may produce an alternating or dynamic pressure that may be additive to the steady state pressure within the combustor. This dynamic pressure may be referred to as combustor acoustics. Relatively high combustor acoustic amplitudes may result in alternating mechanical stress levels that can damage the combustor, related combustor components and other gas turbine engine hardware. Accordingly, combustion acoustics may undesirably limit the operational range of at least some known lean premixed gas turbine combustors. At least some known DLE combustors may be more prone to generate relatively high acoustic levels than other known combustors because DLE combustor acoustics are primarily a non-linear function of the fuel to air ratio (or flame temperature), radial flame temperature profile, and secondarily of the load and other gas turbine parameters. To facilitate reducing combustion acoustics within DLE combustors, at least some known gas turbine engines utilize adjustment of flame temperature profile. Other known gas turbine engines utilize passive means to facilitate reducing the combustor acoustics. However, because of the relatively large number of operational parameters that may affect combustor acoustic generation, measuring combustor acoustics, arresting combustor acoustics that exceed an acoustic threshold value, and maintaining acoustics below the threshold value may be difficult using passive means.